【单选题】Echo-sounder is usually installed at the bottom of observation ship. The water line of ship is 15m. The sound speed is meanly 1500m/s. The time interval between receiving and launching sound wave is 3...
【简答题】Directions: Now, listen to the dialogue again to answer these questions. 1. What is good about a five-disc CD player? 2. Why does the customer like the direct access feature? 3. What kind of CD playe...